CONSERVATION PLAN FOR RIO GRANDE CUTTHROAT TROUT (Oncorhynchus clarki virginalis) IN COLORADO August 23, 2004 Colorado Division of Wildlife Aquatic Wildlife Section Denver, CO CONSERVATION PLAN FOR RIO GRANDE CUTTHROAT TROUT (Oncorhynchus clarki virginalis) IN COLORADO Prepared by: John Alves Doug Krieger Tom Nesler Colorado Division of Wildlife 6060 Broadway Denver, CO 80216 TABLE OF CONTENTS Introduction . 1 Natural History . 1 Taxonomic and Genetic Evaluation . 6 Genetic Management . 7 Management Classifications . 9 Population Viability and Stability . 11 Management of Rio Grande Cutthroat With Regard To Threats . 13 Definitions . 19 RGCT Conservation Strategy . 23 RGCT Five Year Implementation Schedule . 28 Literature Cited . 32 Appendix I. Information About Rio Grande Cutthroat Trout Populations . 36 Appendix II. Status of Rio Grande Cutthroat Trout Populations . 55 Appendix III. Distribution Maps . 60 RGCT Conservation Plan Page ii LIST OF FIGURES Figure 1. Rio Grande Cutthroat Trout Population Types . 57 Figure 2. Distribution of Core Populations . 58 Figure 3. Distribution of Conservation Populations . 58 Figure 4. Distribution of Recreation Populations . 59 Figure 5. Status of Core and Conservation Populations . 59 Map 1:3. Core and Conservation Population Types . 61 Map 2:3. Recreation Population Type . 64 Map 3:3. Core and Conservation Waters by Status Type . 67 LIST OF TABLES Table 1. Distribution of Rio Grande Cutthroat Trout by GMU . 5 Table 2. Summary Report: RGCT Genetic Analysis . .. 40 Table 3. Summary Report: RGCT Core and Conservation Populations . .. 45 Table 4. Summary Report: RGCT Recreation Populations . 48 Table 5. Summary Report: RGCT Status of RGCT Populations . 51 Table 6. Summary of RGCT Management Classifications . 56 Table 7. Status Summary for Core Conservation and Conservation Populations . 57 ACKNOWLEDGEMENTS This conservation plan was developed by personnel of the Colorado Division of Wildlife, and was distributed for internal and external review prior to approval. The CDOW wishes to acknowledge and thank those that contributed to its completion. Bruce May – US Forest Service – Bozeman, MT Marilyn Myers – US Fish & Wildlife Service – Albuquerque, NM David Nickum – Colorado Trout Unlimited – Boulder, CO Barry Wiley – US Forest Service – Monte Vista, CO Peter Wilkinson – New Mexico Department of Game and Fish – Santa Fe, NM RGCT Conservation Plan Page iii INTRODUCTION Rio Grande cutthroat trout, Oncorhynchus clarki virginalis, is the only native salmonid of the Rio Grande basin in Colorado. It is one of four subspecies of cutthroat trout that are native to Colorado’s coldwater streams and lakes. The other three are Colorado River cutthroat (Oncorhynchus clarki pleuriticus), greenback cutthroat trout (Oncorhynchus clarki stomias), and now extinct yellowfin cutthroat trout (Oncorhynchus clarki macdonaldi). Only in southern Colorado and New Mexico can anglers pursue this beautiful sport fish in its native waters. Currently, Rio Grande cutthroat trout occupies significantly less of its historic native range. Many of the populations are restricted to small headwater streams, and some are at risk of extirpation. The Rio Grande cutthroat trout subspecies was not included in the original list of animal and plant species considered warranting protection under the Endangered Species Act of 1973 despite historic declines. In 1973, Colorado independently listed the Rio Grande cutthroat trout as a state threatened species. Recovery goals were established, and after an 11-year period of conservation activities, the subspecies was delisted in 1984 (Colorado Division of Wildlife 1992). Rio Grande cutthroat trout is presently designated a species of special concern in Colorado. Policy of the State of Colorado is that the wildlife and their environment are to be protected, preserved, enhanced, and managed for the use, benefit, and enjoyment of the people of this state and its visitors (Colorado Division of Wildlife Statutes 33-1-101). This document was developed to provide a framework for the long-term conservation of Rio Grande cutthroat trout in Colorado, and represents an extension of previous management plans (Colorado Division of Wildlife 1982, 1992, 1996, 1999). The document will be used to develop management strategies, budgetary needs, and necessary regulations, as well as facilitate cooperative, interagency management of Rio Grande cutthroat trout to conserve and expand new populations. The conservation plan will be reviewed and updated on a 5 year cycle following final approval. NATURAL HISTORY Taxonomy The cutthroat trout, Oncorhynchus clarki, is a prime example of a polytypic species. Cutthroat trout are found in both coastal and inland streams from Alaska to New Mexico, and RGCT Conservation Plan Page 1 within this range the species has evolved into numerous subspecies or geographic races. Many subspecies undoubtedly are polyphyletic, having evolved directly from other subspecies rather than (monophyletically) from a centrally localized stem group. Rio Grande cutthroat trout are believed to have arisen from Colorado River cutthroat trout that entered the previously unoccupied Rio Grande drainage basin during the last glacial period (70,000 years ago) (Behnke 1992). Rio Grande cutthroat trout was first described from “Utah” [Ute] Creek, a tributary of the Rio Grande near Fort Garland, Colorado (Girard 1857). Rio Grande cutthroat trout have red to orange slashes in the gular folds of the lower jaw. They develop colors similar to those of greenback and Colorado River cutthroat trout, but somewhat less intensely than the other two subspecies. Rio Grande cutthroat trout have olive colored backs, light rose to red-orange on the sides to pink or yellowish-orange bellies. Colors are more intense on breeding adults, especially males. Taxonomic differences among cutthroat trout subspecies are based on variation in coloration, spotting pattern, and meristic characters including number of scales in the lateral series, number of gill rakers, number of pyloric caeca, and presence and number of basibranchial teeth. Rio Grande cutthroat trout differ from greenback and Colorado River cutthroat trout by having fewer scales in the lateral series and by the irregular shape of the spots on the caudal peduncle (Behnke 1992). Adult Rio Grande cutthroat trout are distinguished by large, club-shaped spots that are concentrated posterior to the dorsal fin on the caudal peduncle. Basibranchial teeth are weakly developed or absent in Rio Grande cutthroat trout. According to Behnke (1992, 2002), two forms of Rio Grande cutthroat trout exist based on meristic and morphological characteristics. One form associated with the Rio Grande proper of Colorado and New Mexico, and the other with the Upper Pecos River in New Mexico. Behnke determined that the Pecos form had larger spots, which are more typical of greenback cutthroat trout, and more scales in the lateral series. Life History Trout require four kinds of habitat during the various stages of their life history: spawning habitat, nursery or rearing habitat, adult habitat, and over-wintering habitat. Deficiencies in any one of the four will limit populations (Behnke 1992). Specific information on the habitat requirements for spawning, rearing, cover and feeding for Rio Grande cutthroat trout are not available (Rinne 1995). However, Rio Grande cutthroat trout habitat preference is probably consistent with typical cutthroat trout habitat. Cutthroat trout, in general, prefer clear, cold RGCT Conservation Plan Page 2 streams and lakes. Population densities are regulated mostly by stream size and morphology, over-wintering habitat, stream productivity, and summer cover for predator avoidance (Sublette et. al 1990). Optimal cutthroat trout stream habitat is characterized by clear, cold water, a silt free rocky substrate in riffle-run areas; an approximately 1:1 pool-riffle ratio with areas of slow, deep water; well vegetated stream banks; abundant instream cover; and relatively stable water flow and temperature regimes (Raleigh and Duff 1981). Optimal lacustrine habitat is characterized by clear, cold, deep lakes that are typically oligotrophic, but may vary in size and chemical quality, particularly in reservoir habitats. Cutthroat trout are stream spawners and require tributary streams with gravel substrate in riffle areas for reproduction to occur (Hickman and Raleigh 1982). Rio Grande cutthroat trout feed on aquatic invertebrates inhabiting riffle areas of streams, and terrestrial insects that fall into the water (Sublette et. al. 1990). Quality insect production requires rubble-dominated substrate in riffles, oxygenated water and less than 10 percent fines in those riffles. Growth depends primarily on food availability, size of prey, competition, water temperatures, and the length of growing seasons (Behnke and Zarn 1976). Rio Grande cutthroat trout populations inhabiting small streams typically range in size from 2 inches at age 1 to 10 inches at age 7. However, cutthroat trout inhabiting productive lakes attain greater size. Rio Grande cutthroat trout brood fish at Haypress Lake grow to 20 inches and weigh 3.3 pounds (Alves 2002). Spawning occurs in streams from March through July depending on water temperature (usually beginning at 42-48°F), runoff, elevation and latitude (Behnke and Zarn 1976). In Colorado, most spawning occurs from May through July, typically on the descending limb of spring snowmelt when water temperatures near 50 °F. Females mature at three years